1. Field of the Invention
The present invention relates to a method and an engine control unit for operating an internal combustion engine with the aid of data-based models.
2. Description of Related Art
In Otto engines and diesel engines, engine control units are used, among other things, to implement driver command-based torque and rotational speed requests by appropriately adjusting combustion parameters. Because the combustion parameters, however, often do not represent variables that are directly adjustable via control elements, they are adjusted by specifying more readily accessible control variables such as, e.g., the injection quantity, injection point and injection duration, ignition angle, throttle-valve position and the like. In order to implement the torque and rotational speed requests at specific operating points of the internal combustion engine, the control variables are ascertained in an engine control unit with the aid of various characteristic values, characteristic curves, characteristics fields and/or characteristics spaces. The characteristics maps describe correlations between torque requests or rotational speed requests at specific operating points of the internal combustion engine and engine variables, with the aid of which the torque requests or rotational speed requests may be implemented. The characteristics maps may additionally take into account reciprocal dependencies between different engine, combustion, and control parameters, which are required for implementing a control of the internal combustion engine.
The models described by the characteristics maps are characterized by their high complexity since they must normally take into account complex or multidimensional reciprocal internal dependencies of various parameters. For this reason, providing the characteristics maps in an engine control unit involves a correspondingly high memory requirement.
Obtaining the data for preparing these characteristics maps for a particular engine type represents a kind of calibration that is relatively painstaking. This normally requires both the use of special software tools as well as performing extensive tests because especially after an application to a particular engine type the control variables depending on the respective operating point may be changed only to a very small degree or not at all while the vehicle is in operation. The quality of the engine control thus depends directly on the quality of the applied characteristics maps. There are limits to obtaining the mentioned data, which limits depend on capacity on the one hand, while also being a consequence of the general procedure. Thus specimen-to-specimen scatterings, that is, for example, manufacturing-dependent deviations of individual components from the components in the application vehicle in which the data are obtained, normally cannot be taken into account. Moreover, inputting the data ahead of time makes it impossible to take possible aging effects into account, which will only occur when the controlled engine reaches an advanced operating age.
The remaining complexity in a new application or preparation of a data set and structuring of this data set in the form of one or more characteristics maps is nevertheless considerable. The complexity increases further when modern combustion methods are used, which partly involve the requirement of inputting data into the characteristics maps for the engine control in a cylinder-specific manner, which may be required if no cylinder-specific feedback from the combustion chamber is available which could be used as a basis of a control operation. For Otto engines, examples of such new combustion methods are the CO2 emission-reducing CAI method (controlled auto ignition), sometimes also known as gasoline HCCI (homogeneous charge compression ignition), and for diesel engines, the HCCI or pHCCI method (partially homogeneous charge compression ignition), which is used for reducing engine-internal pollutant emissions.
Characteristics maps have particular significance if the engine is operated using a so-called precontrol. Especially in such a case, a disadvantage of conventional engine control systems on the basis of fixed characteristics maps lies in the limited possibilities of an adaptation while the vehicle is in operation, also known as online adaptation. Added to this is the fact that characteristic maps that may be applied at justifiable cost normally only capture the stationary engine operation, while an engine control system is properly challenged only in dynamic operation. This particularly concerns the peaks in pollutant and noise emission in the above-mentioned new combustion methods.
For lack of suitable characteristics maps, the extent to which a dynamic precontrol may be implemented on the basis of characteristics maps is very limited since dynamic measurements for data input are more difficult to implement experimentally and are subject to more unknown influences such as distortions by the dynamics of the sensors used, for example.